I'm not sure what's going on in your situation but if there was a cat5 cable from the cable modem to your NIC and it worked and you then tried to plug it into your hub and it didn't work what's wrong is that you need to have a different cable.
When you connect a computer's network card to a hub you can use a "straight through" cable which means the 1&2 and 3&6 pairs in the cable just go straight through the cable. If you need to connect two NICs or two hubs together you need to use a crossover cable where the 1&2 go to the 3&6 spots.
Most hubs, however, have a crossover port or some button on there that will do it for you. Give that a shot.
To find out if your cable is straight through or crossover take a look at the ends and read off from left to right what colors (and stripes) they are.
Actually my XP computer did work when I plugged the cable modem into the hub (and attached a patch cable from the hub to the XP PC). It was the Win98 computer that didn't work even though a known good patch cable was connected to the hub. I know why, because the NIC card on the XP computer was reconfigured by AT&T for their network while my Win98 still had the original 192.168.0.208 address, obviously installed by the XP networking wizard.
I suppose I would need to get a compatible IP address from AT&T to join their network but I'll need to pay the $9.95. I don't like that solution because I will be doing file-and-printer sharing between the PCs, and with the cable modem plugged in the hub, I am essentially putting my home network on AT&T's local subnet.